Certain types of restaurant have a vocabulary and grammar all of their own. Urban oyster houses are just such. It's all bare brick and scrubbed floorboards. It's men with forearms like oak trees prising meats from shells, and counter service. Eating alone at this sort of oyster house is what the Jews call a mitzvah, a blessing. Or would do if oysters weren't forbidden. My, but the Jewish god is such a terribly picky eater.

The Wright Brothers Oyster & Porter House in London's Borough Market ticks all the boxes. It looks like it was banged together from the contents of an architectural salvage shop over a busy weekend. It has heft and sturdiness. And its oysters are good – the owners have custodianship of stretches of water down in the southwest of England which produce some of the loveliest examples, not least the Duchy natives. And if that suggests an adoration of the bivalves on my part verging on the obsessive, I make no apologies. A taste for raw oysters, for the filthy slap and wash of the sea across your tongue, is one of those indelible markers of adulthood. I'm not sure I could ever really love someone who didn't at least like oysters.

Now Wright Brothers has opened a second outpost. There are tables upstairs, but downstairs it is all freestanding counters and an open kitchen, giving a top view of some hot man-on-shellfish action. It is self-consciously laid-back, an exercise in nose thumbing at fancier joints. This brings with it a few issues, not least over price. At the heart of the menu is a do-it-yourself fruits de mer – you put together a platter of crab, razor clams, whelks, etc.

This does mean you can see the pricing of everything, and some of it is over the odds. They charge £4 for a pleasing but not especially large langoustine. At Scott's and J Sheekey's they charge £3.75; at Terence Conran's equally high-end Boundary they cost £3.33. Likewise, while their native-oyster pricing is pretty much on par, what they don't have on their standard menu are any of the cheaper rock oysters. It makes eating here look a little exclusive, and unnecessarily so. That said, the Duchy natives and some small sweet Kumamotos, usually only found in the Pacific northwest, delivered exactly what we were looking for.

The rest of the menu is a mixture of standards, like fish pie and whitebait, and more evolved dishes. Charging £9 for rather good crispy squid looks opportunistic. By contrast, £11.50 for a big bowl of their thick, luscious fish stew, the liquor boasting a big peppery end and swimming with shellfish, was a bargain. I was less keen on their sardines on toast, each opened out and spread with a thick garlic and parsley persillade, and grilled. Sardines are butch little blighters which can take some serious heat. More concerning to me was the portion size. There's no point pretending that the restaurant didn't know what I was doing there. I have met one of the owners, and he happened to be by the door when I arrived. So did that explain why everyone else who ordered the sardines got two on toast, and I got three? If I hadn't been sat by the kitchen I might not have clocked the true size of the dish, and might have assumed it was better value than it actually is.

This works both ways, because our service was not all that. Finger bowls were not delivered with our langoustine, and our wine order was completely forgotten. If this happens to me when they know what I'm doing there, what does it say about the service for others? At the prices they are charging, these things shouldn't happen to anybody. Wright Brothers Soho is a welcome addition to the offerings in central London. It could be superb. But to become that it really does need to fine tune what it's doing. Or, to overextend a metaphor, it may have got its vocab and grammar right, but its accent is just not pitch perfect.